1. Folds Faults and Mountains

2. Fold and Thrust Mountains
Enormous mountain ranges form when plates converge.
Contorted rocks show the power of plate tectonics.

3. Rock Distortion

4. Convergent Plate Boundaries and Folding
Continent-Continent
collision forms
Folded Mountain Belt:Alps, Himalayans, Appalachians
Ocean-Ocean
collision forms
Island Arc: Japan,
Aleutians, Cent. Am.

5. Evidence of Lateral Compression
Formerly horizontal layers are twisted, bent, or broken.
Some folded rocks are pushed over on their sides, or even upside down.

6. Source: Martin Bond/Science Photo Library/Photo Researchers, Inc.
Folded Sandstone
Source: Martin Bond/Science Photo Library/Photo Researchers, Inc.

7. Studying Faults and Folds
The branch of geology that studies crustal deformation is called Structural Geology.
Geologic structures determine ground stability, and where to build cities.

8. Stress Units are Pressure: Force/Area Three types of stress
a) Compression causes bending
b) Tension causes thinning
Shearing causes one type of faults

9. Compression, Tension, and Shearing Stress
Convergent Divergent Transform

10. Types of deformation Elastic deformation up to elastic limit
Springs back to original shape Demo: Pencil
Brittle failure (it breaks) Demo Pencil
Causes: 1. subjected to great stress that exceeds the yield point AKA elastic limit, OR
Subjected to sudden stress AKA “impact”
Plastic deformation
Does not spring back … keeps deformed shape
Demo Chewing gum
Cause can be high temperature – near melting
or high pressure … squeezed like a ball of clay

11. Relationship Between Stress and Strain
Strain can be a change in shape (a deformation) due to an applied stress

12. Relationship Between Stress and Strain at low Temps and Pressure or Sudden Stress

13. Relationship Between Stress and Strain under high Temps or Pressure

14. Factors affecting rock deformation
Intensity of applied stress
Heat –Temperature of the Rock
Amount of Time the Stress is applied
Rock Composition

15. Interpreting Deformed Rocks
Most apparent in sedimentary rocks
Importance of deformation
Indicates past plate motions
Indicates other past geological events
Locates specific natural resources
Mapping 101: Rock orientation: strike and dip

16. Strike and Dip
Strike is long line, dip is short line
Note the angle of dip given 45o
Strike intersection w horizontal, dip perpendicular, angle from horizontal down toward surface

17. Folds Folds def: Bends in rock layers Types: synclines and anticlines
Syncline (downfold) innermost rocks youngest
Anticline (upfold) innermost rocks oldest
Parts of a fold (limbs, axial plane, axis)
Note: Anticlines and synclines are structures in rocks, not surface landforms

18. Folded Rocks, Hwy 23 Newfoundland, New Jersey
Note highest point
Adjacent Anticline and Syncline
Source: Breck P. Kent

19. Folded Rocks (Dorset, England) Center has overturned area
Older
Overturned
Area
Younger
Lucky we have ways of recognizing right side up
What are they?
Source: Tom Bean
Younger
Older

20. Folded Rock Before Erosion

21. Folded Rock After Erosion
Eroded Anticline, older rocks in center. Syncline is opposite.

22. Topography may be opposite of Structure Anticline Before/After Erosion
Notice center rock oldest

23. Topography may be opposite of Structure Syncline Before/After Erosion
Notice center rock youngest

24. Fold symmetry a) Symmetrical or open folds b) Asymmetrical folds
c) Overturned folds
d) Recumbent folds
e) Plunging folds

25. Various Folds

26. Various Folds (cont'd)

27. Various Folds (cont'd)

28. Various Folds (cont'd)
Not a good drawing, axial plane should be closer to horizontal

29. Plunging Folds Up End Down End
Demo: Plastic box, water, paper folds Up
End
Down
End
Nose of anticline points direction of plunge, syncline nose in opposite direction

30. Source: GEOPIC©, Earth Satellite Corporation
Plunging Folds
Source: GEOPIC©, Earth Satellite Corporation

31. Interpreting Folds
Determine if center rocks are older or younger than flanks: fossils, right side up clues (graded bedding and mudcracks)
Are limbs parallel or “Nosed”?
Determine limb dips from measurements, stream V’s. Strike and Dip
Use nose rules for anticlines and synclines

32. Again: Strike and Dip

33. Domes and basins 1. Domes 2. Basins 3. Occur within plates
4. Result from vertical forces
5. Geographic examples (later)

34. 3-D: Dome and Basin

35. Fractures Fractures - Joints: fractures with no relative movement
- Faults: fractures with relative movement

36. Joints: Fractures – with no movement
Source: Martin G. Miller/Visuals Unlimited

37. Fault Type 1 - Dip-slip faults
1) Terms: Hanging wall and footwall
2) Normal faults
(a) Grabens
(b) Horsts
3) Reverse faults
a) low angle called Thrust faults
4) Oblique-slip faults

38. Dip-Slip Faults

39. Normal Fault: Hanging Wall Down
Hanging wall overhangs the fault plane
Key
Bed
Source: John S. Shelton
Especially common in divergent margins

40. Normal Fault (Hanging Wall down)

41. Reverse Fault (called “Thrust Fault” if shallow angle)
Typical of convergent margins
(Hanging wall Up)
Structural Geology is taught by Dr. Krall
Younger
What phase of magma fractionation would result in the placement of this ore body?
Which formed first, the ore body or the fault?
What common mineral is mostly likely in the ore body?
Miners pay geologists to find their lost orebody
One friend earned enough to buy a house
This poor guy is out of luck

42. Evidence of faults a) Visible displacement of rocks
b) Pulverized rock and “Slickensides”
c) Key beds cut out by faulting reappear elsewhere.

43. Fracture Zones and Slickensides

44. Types of Faults - 2 Strike-slip faults 1
1) Example: San Andreas Transform fault
Distinctive landforms (linear valleys, chains of lakes, sag ponds, topographic saddles)
Fresh pulverized rock. Transform fault through granite: Arkose sandstone
Evidence of Shear stress

45. Source: Georg Gerster/Wingstock/Comstock
San Andreas Fault
Source: Georg Gerster/Wingstock/Comstock

46. Horizontal Movement Along Strike-Slip Fault

47. Oblique Slip Also seen in Transform Faults such as San Andreas
Both strike slip and dip-slip
Also seen in Transform Faults such as San Andreas

48. Types of faults Strike-slip faults 2
1) Example: Mid-Ocean Ridge Transform faults
Small offsets in ridge
San Andreas is also ridge offset,
but on a huge scale with a historical twist

49. Faults & Plate Tectonics
Divergence
Convergence
Transform

50. Plate tectonics and faulting
Normal faults: mid-ocean ridges and continental rifts are the same thing.
Divergent Margins
Surface rock is pulled apart
Hanging wall drops down

51. Horst and Graben Formation

52. Horst and Graben Formation

53. Source: Simon Fraser/Science Photo Library/Photo Researchers, Inc.
Graben in Iceland
Source: Simon Fraser/Science Photo Library/Photo Researchers, Inc.

54. Plate tectonics and faulting
Reverse and thrust faults: convergent plate boundaries
Hanging Wall is pushed up.

55. Lewis Thrust Fault

56. Lewis Thrust Fault (cont'd)

57. Lewis Thrust Fault (cont'd)
Source: Breck P. Kent
PreCambrian Limestone over
Cretaceous Shales

58. Plate tectonics and faulting
c) Strike-slip faults: Transform Boundaries

59. San Andreas Fault

60. Types and processes of mountain-building (Orogenesis)
1. Volcanic mountains
2. Fold-and-thrust mountains
3. Fault-block mountains
4. Upwarped mountains

62. Types of Mountains 2. Fold-and-thrust mountains
Formed by Continent-Continent Collisions

63. Appalachian Mountain System

64. Model for the Evolution of the Southern Appalachians
Supercontinent breaks up, rifts apart.
rift
Another
Rift
Over here somewhere
Another rift starts moving Africa west. The ocean floor breaks
and one side subducts, starting a new island arc.

65. Model for the Evolution of the Southern Appalachians (cont’d)
The ocean floor breaks again, new subduction adds volcanics to an existing microcontinent
Weak rifts
Net westward movement pushes the ridge, subduction zone and fragment into N.America
Rifting restarts to the East

66. Model for the Evolution of the Southern Appalachians (cont’d)
Arc and subduction zone collide w/ N.Am., westward subduction starts
The continents collide

67. Model for the Evolution of the Southern Appalachians (cont’d)
Rifting Restarts

68. Collisional Mountains ??? (The Grand Tetons in Wyoming)
Source: Peter French/DRK Photo
Paradigm shifts: What is wrong with our model? More on this later

69. Fault-block mountains
Rift Valleys, Mid Ocean Ridges
Basin and Range province ???
Normal Fault Blocks as in East Africa
Divergent Margins?
Paradigm Shifts

70. Origin of the Basin and Range Southwestern North America Looks different
Paradigm Shifts

71. Upwarped mountains a) Gently bent without much deformation
b) Ascent of buoyant mantle material
c) Far from plate boundaries
d) Adirondack Mountains: Uplift of deep PreCambrian Igneous and Metamorphic rocks

72. The Adirondack Mountains of Northern New York
Source: Clyde H. Smith/Allstock/Tony Stone Images

73. Anticlines and Oil
Early USA petroleum exploration, e.g. Pennsylvania anticlines

74. Faults and Oil

75. End of Chapter 9